BUG #1645: Blank spots on solid fillareastyle with fillareaindices

The solid fillareastyle was treated as a pattern style in that
each level was extracted and rendered individually. Because of a
bug in vtkBandedPolyDataContourFilter lower isocontours differ
from upper isocontours which results in blank spots. In this fix
we trigger merging of levels which fixes the problem for solid fill.
We'll fix the problem for pattern fill in a subsequent commit.

Packages/vcs/Lib/vcsvtk/isofillpipeline.py

@@ -93,9 +93,11 @@ def _plotInternal(self):
         tmpColors = []
         tmpIndices = []
         tmpOpacities = []
-        indices = self._gm.fillareaindices
-        opacities = self._gm.fillareaopacity
         style = self._gm.fillareastyle
+        # levels would not be merged if the user sets fillareaindices for a 
+        # 'solid' style resulting in a less efficient plotting.
+        indices = (None if (style == "solid") else self._gm.fillareaindices)
+        opacities = self._gm.fillareaopacity
         if indices is None:
             indices = [1]
         while len(indices) < len(self._contourColors):
@@ -179,7 +181,7 @@ def _plotInternal(self):
             for j, v in enumerate(l):
                 cot.SetValue(j, v)
             cot.Update()
-
+            
             cots.append(cot)
             mapper.SetInputConnection(cot.GetOutputPort())
             lut.SetNumberOfTableValues(len(tmpColors[i]))
@@ -321,7 +323,7 @@ def _plotInternal(self):
                                            self._contourColors, legend,
                                            self.getColorMap(),
                                            style=style,
-                                           index=self._gm.fillareaindices,
+                                           index=indices,
                                            opacity=opacities))
 
         if self._context().canvas._continents is None: